Systems and methods for providing optimized taxiing path operation for an aircraft

ABSTRACT

A taxiing path optimization system is provided for computing a taxi path of an aircraft using available taxi routes of a corresponding airport. An interaction means management unit manages interactions between a user and the taxiing path optimization system using an interactive device for inputting a taxi clearance. An aircraft positioning management unit manages positional information of the corresponding airport and aircraft received from a plurality of sources for augmenting an aircraft position by consolidating the aircraft position with the positional information in a complementary fashion. A taxi path display unit displays the taxi path based on the inputted taxi clearance and the augmented aircraft position, wherein the taxi path is automatically computed based on aircraft characteristics or airport capabilities.

CROSS-REFERENCE

This application is a Division of co-pending U.S. patent applicationSer. No. 14/565,964 filed Dec. 10, 2014.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to aircraft taxiing systems,and in particular relates to a taxiing path optimization system for anaircraft using positioning data collected from various sources.

BACKGROUND OF THE INVENTION

To assist in navigation in an airport, a process of taxiing typicallyincludes receiving a clearance from an air traffic controller (ATC),checking the received clearance, entering the received clearance into anavigation system for displaying the clearance on a map, and building ataxi route from a current position to a destination position, forexample, on a runway or at a parking gate.

In preparation for the taxiing, flight crews perform several tasks. Thecrews determine an accurate position of the aircraft by observing itsexternal surroundings and/or a map. Then, the crews find and monitor ataxiing path based on the ATC clearance while monitoring an outsideevents and movements for preventing collision with other aircraft orequipment. Further, the crews prepare the aircraft for optimizing thetaxiing path according to ATC constraints. As a result, the workloads ofthe flight crews become significant and convoluted during airportsurface operations.

It is important that the taxiing operation is performed smoothly withoutany interruptions and delays. An optimization of the taxiing operation,for example, from the runway to the gate (i.e., taxi-in) and from thegate to a line-up on the runway (i.e., taxi-out), is also critical forthe efficiency of the airline and airport operations. Today, certainconventional applications are provided for an effective taxingoperation, but these applications are not accurate enough and aredata/time consuming.

As an example, an airport database specification developed by anAeronautical Radio, Incorporated (ARINC), namely ARINC 816, defines anembedded interchange format for Airport Mapping Database (AMD). TheARINC 816 standard proposes a way to describe airport elements, such astaxiways, runways, parking areas, stands, buildings, roads, obstacles,and the like. Specifically, ARINC 816-0 provides geometricaldescriptions with points, lines and polygons used for displaying airportmaps on on-board displays. ARINC 816-2 provides additional objects, suchas nodes and edges (or links between two nodes) for describing a flowgraph of the airport.

Further, the ATC provides a taxi clearance to the flight crews via radioor datalink communication services. The taxi clearance includesinformation about a departure point, successive airport elements, and adestination point in a particular order. Specifically, the taxiclearance has a set of airport element names indicating the departureand destination points, and any elements therebetween (e.g., E60 (via)P10 P40 W30 (to) 14L, where E60 denotes the departure point, 14L denotesthe destination point, and P10, P40, and W30 denote the successiveelements). Based on this taxi clearance, a taxi route is entered into anon-board avionics system using a keyboard, a datalink, or other suitableelectronic devices (e.g., a color-coded electronic chart developed byJeppesen®). The taxi route represents an on-ground trajectory of theairport, including a set of identifiers or a set of point coordinates,continuously connecting two extremities (e.g., the departure anddestination points).

In the aircraft, an ownship position is determined by various sensors,such as an Inertial Reference System (IRS) or a Global NavigationSatellite System (GNSS), or some radio navigation devices (VHFOmnidirectional Range, Distance Measuring Equipment) or any combinationof above-mentioned systems and devices. The ownship position istypically displayed on the on-board avionics system for navigationpurposes, and provides a map which represents the aircraft surroundingswithin a predetermined range. To generate the taxi route, the flightcrew receives the taxi clearance and writes it on a piece of paper.Next, the crew uses an airport paper map to find the taxi route tofollow.

Alternatively, the crew uses the Jeppesen® chart to highlight a path ona digital map as if the crew draws the path with a pen, but the pilotmust enter the clearance into the system using the keyboard or othersuitable tactile interactive devices for computing the correspondingtaxi route on the digital map for display. This manual process ofentering the sequence is slow and cumbersome because the clearance needsto be continuous (i.e., each clearance element must be connected to asuccessive one). For example, if the taxi clearance sequence is long,ensuring the continuity of the clearance sequence takes time when usingthe keyboard. Further, aircraft characteristics, such as its AircraftClassification Number (ACN), maximum limitations concerning itswingspan, and its Pavement Classification Number (PCN) are not includedin computing the taxi route.

Generally, the flow graph of the airport is described through the nodesand edges, which are tightly integrated with other geometrical objects.For example, the nodes and edges are attached to containers, whichcontain objects related to a given element. A runway container containsa runway surface geometry, a runway center line geometry, runwaythresholds, runway markings, nodes and edges related to this particularrunway, and the like. Thus, the flow graph of the airport includesunnecessary geometrical descriptions of the airport, causing memoryspace waste, longer computation time, and redundant complexity forgenerating the taxi route. Further, because this type of flow graph doesnot include an explicit connectivity of each edge, the associatedapplication must determine to which set of edges a given edge isconnected, thereby causing additional computation time. Typically, thistype of flow graph only includes taxiways and runways, and does not haveparking apron and deicing areas, making it impossible to compute thetaxi route from or to a gate or a parking stand.

Another disadvantage of the conventional application is that when asystem of visualization of the taxi clearance is available in thecockpit via the avionics system or an Electronic Flight Bag (EFB)system, the flight crews often must use a piece of paper to write downthe clearance before entering the clearance into the system, andexplicitly advise the avionics system that the pilot will manually enterthe clearance. Modern tactile tablets, such as iPad® or laptops with atouch-sensitive screen, can support the EFB system for managingdocuments, aircraft libraries, manuals, and the like. However, thedrawback of Component On-The-Shelf (COTS) tablets is that a GNSSposition provided by the tablets does not satisfy mandated accuracyrequired in the aviation rules and regulations, such as a generalacceptable means of compliance for airworthiness of products, parts andappliances, namely AMC 20-25.

All these steps take additional time and increase workload during thetaxiing operation while the pilot simultaneously performs other tasks,such as checking and controlling the aircraft, communicating with groundpersonnel, performing surveillance tasks, and the like. These additionaltasks can be a source of potential errors, and may require significanttime and effort to correct mistakes while listening to ATC instructions,thereby increasing operation costs. Therefore, there is a need fordeveloping an improved taxiing system and method such that the taxiingsystem facilitates an accurate guidance of the aircraft for reliableon-ground navigation and control, using a standardized airport database.

SUMMARY OF THE INVENTION

Advantages are achieved by the present taxiing path optimization systemwhich includes an improved Airport Graph Database (AGDB) for storingspecific information relating to geographic and geometric relationshipsbetween an aircraft and its surrounding objects in a two orthree-dimensional coordinate system. The present taxiing pathoptimization system further includes a computer processor coupled todatabases and programmed to perform tasks and display positionalinformation of airport elements and paths. Included in the present AGDBis a description of an airport flow graph, and is designed to take upminimal space in memory such that it can be readily embedded indifferent applications, such as avionics systems in an aircraft.

For example, positional information representing parking stands, deicingareas, landscape, buildings, airports, runways, taxiways, terminalgates, obstacles, approach profiles, flight paths, and the like iscollected or compiled from various sources, such as satellites, internetapplications, and airport databases. Such information is stored ineither onsite or remote databases, and as described in greater detailbelow, various functions can be performed for flight crew members onboard by displaying reliable, real time accurate data. It is preferredthat the present AGDB is self-sufficient with such information, and doesnot rely on other databases. Further, the present AGDB can be used withother on-board and on-ground applications, such as the ATC systems fordisplaying airport elements, or generating taxi clearances or routes.

As discussed in greater detail below, the present taxing pathoptimization system provides an enhanced support function for taxiingoperations with an optimized dynamic behavior of the taxi path updateusing various positioning sources and augmented algorithm techniques. Ina preferred embodiment, it is contemplated that a system and method isprovided for processing multiple sources of data for positioning of theaircraft using at least one of an internal or external GNSS sensor, ageometric layout data system, an Automatic dependentsurveillance-broadcast (ADS-B), a wireless technology (e.g., Wifi), andthe like.

Also included in the present taxiing path optimization system is that asystem and method configured for correlating various sources ofpositioning data with the geometric topology of an airport layout.Further, the present taxing path optimization system provides enhanceddisplays and updates of the taxi path based on GNSS positions related tothe airport elements and the aircraft in real time.

The present taxing path optimization system automatically generates thetaxi route for the aircraft based on the positional information. As aresult, a stable and efficient taxi route is maintained during taxiing,and a reliable on-ground navigation is provided while the aircraft ismoving on a runway or taxiway, or when the aircraft is in a standby modeat a terminal gate or on the runway or taxiway. Thus, the present taxingpath optimization system provides a reliable means of assisting in theoperation of the aircraft during on-ground taxing or while being parkedat the terminal gate or other locations at the airport.

Other advantages of the present taxing path optimization system include,as described in greater detail below, a pre-computed connectivity ofeach link and a pre-computed dual relationship between points and nodes,curves and links, and links and airport elements. Because the presentoptimization system enables the flight crew member to quickly enter ataxi clearance during a taxi phase, the operation time, costs, andworkload are reduced significantly. Since the taxi clearance input doesnot have to be complete or continuous, and the present optimizationsystem automatically constructs the taxi clearance by filling inpotential gaps, the crew can quickly select the taxi clearance byentering only a portion of the entire taxi clearance. For example,entering only the departure and destination elements suffices, andintermediate clearance elements between the departure and destinationelements are automatically generated by the present optimization system.As a result, the next element entered in the taxi clearance does notneed to be contiguous to the previous element because the presentoptimization system automatically fills in the elements between adjacentelements.

In one embodiment, a taxiing path optimization system is provided forcomputing a taxi path of an aircraft using available taxi routes of acorresponding airport. An interaction means management unit managesinteractions between a user and the taxiing path optimization systemusing an interactive device for inputting a taxi clearance. An aircraftpositioning management unit manages positional information of thecorresponding airport and aircraft received from a plurality of sourcesfor augmenting an aircraft position by consolidating the aircraftposition with the positional information in a complementary fashion. Ataxi path display unit displays the taxi path based on the inputted taxiclearance and the augmented aircraft position, wherein the taxi path isautomatically computed based on aircraft characteristics or airportcapabilities.

In another embodiment, a method of computing a taxi route for anaircraft is provided. The taxi route represents an on-ground trajectoryof an airport during taxiing operations utilizing a taxiing pathoptimization system. Included in the method are building adisplay-independent and geometrically-based database for describing aflow graph of the airport, the database representing a description ofall potential taxi ground trajectories for the aircraft; receiving aninitial taxi clearance having airport elements, the taxi clearance beinginputted by a user or a related system based on information stored inthe database; modifying the initial taxi clearance by eliminatingambiguous taxi routes caused by the initial taxi clearance, and byresolving gaps between the airport elements in the initial taxiclearance; and finalizing the taxi route based on the modified taxiclearance for on-ground navigation of the aircraft at the airport.

In yet another embodiment, a method of computing a taxi route for anaircraft is provided. The taxi route represents an on-ground trajectoryof an airport during taxiing operations utilizing a taxiing pathoptimization system. Included in the method are receiving an initialtaxi clearance having a list of taxi clearance elements including atleast two airport elements; searching for links between successive pairsof nodes defined by the list of taxi clearance elements using apredetermined algorithm; generating a set of links connecting the nodesbased on the searched links; automatically generating at least oneairport element for filling in gaps between unconnected airportelements; consolidating the initial taxi clearance with the generatedairport elements; and discretizing the set of links into X/Y points as afinal taxi route representation for the aircraft.

The foregoing and other aspects and features of the disclosure willbecome apparent to those of reasonable skill in the art from thefollowing detailed description, as considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary visualization of the present taxiingpath optimization system;

FIG. 2 is a flow chart of executing the present taxiing pathoptimization system;

FIGS. 3-7 illustrate exemplary visualizations of various airport layoutsand displays being used as the background maps of the present taxiingpath optimization system;

FIG. 8 illustrates an exemplary visualization of a geometrical part of aflow graph with a satellite background;

FIG. 9 illustrates an exemplary visualization of a logical part of aflow graph with identifiers;

FIG. 10 illustrates exemplary exhaustive potential on-groundtrajectories of a corresponding aircraft during taxiing operations;

FIG. 11 illustrates connectivity examples using Bézier curves;

FIGS. 12 and 13 illustrate exemplary connectivity links used in thepresent taxiing path optimization system;

FIGS. 14-21 illustrate an exemplary combinational use of a Smart Fingersystem and a virtual keyboard for the present taxiing path optimizationsystem;

FIGS. 22-24 illustrate an exemplary method of determining a consolidatedaircraft position using a five-step method of the present taxiing pathoptimization system;

FIG. 25 is a flow chart of computing or generating a final taxiclearance and corresponding taxi routes using the present taxiing pathoptimization system;

FIGS. 26 and 27 illustrate an exemplary method of searching for a pathbetween successive pairs of nodes using the present taxiing pathoptimization system;

FIG. 28 illustrates an exemplary method of displaying a taxi clearancesequence on a display using different colors;

FIG. 29 illustrates an exemplary Bézier curve having discretized links;

FIGS. 30-32 illustrate an exemplary taxi clearance input method usingthe Smart Finger system of the present taxiing path optimization system,featuring an automatic fulfillment of the gaps between elements; and

FIGS. 33-35 illustrate an exemplary method of displaying multiplepossible taxing paths when the inputted taxi clearance is ambiguoususing the present taxiing path optimization system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present disclosure are described below byway of example only, with reference to the accompanying drawings.Further, the following description is merely exemplary in nature and isin no way intended to limit the disclosure, its application, or uses. Asused herein, the term “module” or “unit” may refer to, be part of, orinclude an Application Specific Integrated Circuit (ASIC), an electroniccircuit, a processor (shared, dedicated, or group) and/or memory(shared, dedicated, or group) that executes one or more software orfirmware programs, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality. Thus, while thisdisclosure includes particular examples and arrangements of the modules,the scope of the present system should not be so limited since othermodifications will become apparent to the skilled practitioner.

Referring now to FIG. 1, the present taxiing path optimization system isgenerally designated 10, and is designed to provide an efficient way tocompute an aircraft taxi path using a display of taxi routes on top ofvarious airport layouts. In one embodiment, the taxi path is displayedon an electronic chart of the airport. In another embodiment, the taxipath is displayed on an airport map compatible with industryrequirements for airport mapping databases for aeronautical use (e.g.,ED 99C) and the ARINC 816-0 standard established by Radio TechnicalCommission for Aeronautics (RTCA). In yet another embodiment, the taxipath is displayed on a conformal display for guidance purposes, forexample, in a Head-up Display (HUD) or a Synthetic Vision System (SVS).As a result, the present taxiing path optimization system 10 provides ascalable way to manage the taxiing operations with various options tosuit different applications.

Included in the present system 10 are an interaction means managementsystem or unit 12 (Part A), an aircraft positioning management system orunit 14 (Part B), and a taxi path display system or unit 16 (Part C).The interaction means management system 12 manages interactions betweenflight crew members and the present system 10 by way of a human machineinterface (HMI), such as a keyboard, a touch sensitive pad or screen, avoice recognition system, and the like.

As discussed above, when the flight crew receives the taxi clearancefrom the ATC, the crew manually computes the taxi path at the beginningof the taxiing and during an execution of a taxing phase, such astaxi-out and taxi-in. The term “taxi-out” generally refers to aircraftnavigation from any parking stand until a line-up on a runway. The term“taxi-in” generally refers to the aircraft navigation from the runway toan arrival at a parking site or a designated gate.

In Air Traffic Management (ATM), certain airports are equipped withrouting functions for allowing a routing computation of the taxi path inadvance (e.g., before the push back and before landing). This preplannedtaxi path can be sent directly from the airport to the aircraft if thedatalink (or the datalink communication service) is available, and alsovia an airline flight operation if there is a sharing of the routingdata information among the airport stakeholders (e.g., an airport orairlines).

Included in the interaction means management system 12 are interactive(e.g., textual and graphical) devices configured for receiving an inputsignal from the crew. In one embodiment, the crew uses his or her ownfinger, namely a “Smart Finger” system, to graphically interact with thepresent system 10. Optionally, the crew outspokenly states the taxi pathinto a vocal recognition system. It is also contemplated that an eyetracking mechanism is provided for allowing the present system 10 todisplay the taxi path based on eye movement correlated with a layout ofthe airport.

The interaction means management system 12 takes advantage of thedatalink capabilities to automatically receive the taxi clearance fromthe ATC if the airport is equipped with the datalink. The taxi clearanceis generally received in a dedicated Communication Management Unit (CMU)and then transferred to a tablet via an Aircraft Interface Device (AID).A dedicated airline datalink can be used for the airline flightoperations. A collaborative airport database reachable by the aircraftcan also be used for a routing service in exchange of the preplannedroute.

The aircraft positioning management system 14 manages GNSS informationreceived from multiple sources using the tablet or via aircraftinterfaces. The GNSS information can be received from at least one of abuilt-in GNSS positioning system of the tablet, an external GNSS sensorconnected to the tablet to increase accuracy, and an internal aircraftGNSS positioning system via the AID. Each GNSS source operates in acomplementary fashion to provide accurate positional information of theaircraft during taxiing operations.

Specifically, the aircraft positioning management system 14 is designedto interface with other data sources for augmenting the accuracy andintegrity of the aircraft position. In one embodiment, the aircraftpositioning management system 14 utilizes an Automatic DependenceSurveillance Broadcast Data (ADS-B IN). While the ADS-B IN data is usedto display the surrounding traffic on a graphical display, the aircraftpositioning management system 14 extracts an ownship position data fromthe ADS-B IN data. This position data is used in an augmented algorithmto consolidate the aircraft position information with other sources toincrease the accuracy and integrity of the aircraft position. The ADS-BIN data can be received from at least one of an internal ADS-B sensorbuilt-in the aircraft hardware, an external ADS-B sensor connected tothe aircraft hardware, and an Aircraft Interface Device (AID) if theaircraft is equipped with the ADS-B IN capability.

In another embodiment, the aircraft positioning management system 14interfaces with a wireless communication facility, such as a Wifi accesspoint, and performs a geo-localization for determining the aircraftposition. This Wifi data is also used in the augmented algorithm toconsolidate the aircraft position information with other sources toincrease the accuracy and integrity of the aircraft position. Otherairport facilities, such as radar, can also be used in determining theaircraft position if the airport is equipped with a ground surveillanceinfrastructure. The aircraft positioning management system 14 receivesthe aircraft position information from the various sources as describedabove, and augment the accuracy and integrity of the aircraft positionalinformation. Optionally and under previously defined conditions, theflight crew member has an option to selectively activate or deactivatecertain data sources based on an operational experience during apredetermined period.

The taxi path display system 16 provides at least four levels of displayoptions for displaying the taxi path based on the quality (e.g.,integrity and accuracy) of the aircraft positional information using theCOTS tablet. Other suitable display devices are contemplated to suit theapplication. A first level of display option provides a static displayof the taxi path without the aircraft position. The taxi clearance isentered and updated manually by the crew without any automation forupdate of the taxi path. This option is always available for the crew,and takes advantage of the interaction means as described in theinteraction means management system 12 (Part A).

In a second level of display option, the GNSS position is at leastpartially available, but no GNSS position is guaranteed. Specifically,it is not feasible to display the ownship position as realized in anAirport Moving Map (AMM) application as an industry certificationconstraint is not met (e.g., as mandated in the AMC 20-25). However, inthis option, the present AGDB is utilized for displaying the taxi pathupdate based on the GNSS positional information, the augmentation of theGNSS position (if available), and the correlation of the topology of theairport layout. Optionally, no aircraft symbol is displayed, but therepresentation of the taxi path is progressively truncated in relationwith the progress of the aircraft taxiing.

In a third level of display option, the GNSS position is available andthe GNSS performance is guaranteed to meet the certificationrequirement. The aircraft position is displayed on an airport maplayout. The use of the algorithms, such as those used to improve theaircraft positional information, allow an optimal representation of theownship position and the taxi path.

A fourth level of display option corresponds to the GNSS position andthe taxi path with a level of GNSS performance for allowing the guidanceof the aircraft. This level allows potential uses and benefits for lowvisibility operations or for automatic guidance if the taxi trajectoryis coupled with an Automatic Pilot for ground control.

Referring now to FIG. 2, an exemplary method of executing the presenttaxiing path optimization system 10 is illustrated. Although thefollowing steps are primarily described with respect to the embodimentsof FIG. 1, it should be understood that the steps within the method maybe modified and executed in a different order or sequence withoutaltering the principles of the present disclosure.

The method begins at step 100. In step 100, the present taxiing pathoptimization system 10 builds an improved display-independent andgeometrically-based Airport Graph Database (AGDB) for describing a flowgraph of a corresponding airport. It is also contemplated that the AGDBis built off-line, and the present taxiing path optimization systemloads the AGDB built off-line. The present AGDB represents a descriptionof all potential taxi ground trajectories or routes that could take theaircraft, using a geo-referenced geometrical description and a logicalflow graph description, including taxiways, runways, parking areas,deicing points, and the like. Included in the flow graph are nodes,links (or edges) between two nodes, and elements. Each element includesa continuous set of links describing an airport element, such astaxiways, runways, parking area, and the like.

The flow graph may include a geometrical description of possibletrajectories of the aircraft on the ground, and has points (i.e.,geo-referenced points) and curves (i.e., mathematical lines defined by aset of points). In a preferred embodiment, the Bézier curve algorithm isused to define a smooth curve, but other suitable curve algorithms, suchas B-splines, or Nonuniform Rational B-splines (NURBS) algorithms, arealso contemplated.

A Bézier curve is comprised of a set of control points which define thesmooth curve that can be scaled indefinitely. For example only, eachBézier curve may be defined by polynomial equations, as provided byexpression (1):

B(t)=Σ_(i=0) ^(n) b _(i,n)(t)P _(i) ,tε[0,1]  (1)

where P_(i) are the control points of the Bézier curve, b_(i,n) are theBernstein base polynomials of degree n defined as provided by expression(2):

$\begin{matrix}{{{b_{i,n}(t)} = {\begin{pmatrix}n \\i\end{pmatrix}{t^{i}\left( {1 - t} \right)}^{n - i}}},{i = 0},\ldots \mspace{14mu},n} & (2)\end{matrix}$

In a preferred embodiment, the 1^(st) and 3^(rd) orders of Bézier curvesare used, but other orders (e.g., higher orders) are also contemplated.For example only, exemplary first and third orders of the Bézier curvemay be defined as provided by expressions (3) and (4):

-   -   1^(st) order Bézier curve, representing a straight line, is        defined as

B(t)=(1−t)P ₀ +tP ₁  (3)

-   -   3^(rd) order Bézier curve, representing a smooth curve, is        defined as

B(t)=(1−t)³ P ₀+(1−t)² tP ₁+(1−t)t ² P ₂ +t ³ P ₃  (4)

A primary use of the present AGDB is to support a computation of taxiroutes (i.e., ground trajectories). The computed taxi routes aredesigned to accurately support a ground guidance of the aircraft,ensuring appropriate data accuracy and integrity of industrializationprocess requirements. Another use of the present AGDB is to display ataxi route, which is display-independent, and thus various backgroundmaps can be used for simultaneous display, e.g., in conjunction with anAirport Mapping Database (AMDB), Navtech® eCharts, satelliteorthoimages, and other suitable geo-reference backgrounds. Further, thecomputed taxi routes take into account aircraft capabilities, such asthe ACN, PCN, a turning radius and a maximum wingspan of the aircraft.

Referring now to FIGS. 3-7, examples of various airport layouts anddisplays are illustrated for use as the background maps of the presenttaxiing path optimization system 10. FIG. 3 illustrates an exemplaryAMDB background map. FIG. 4 illustrates an exemplary eCharts backgroundmap. FIG. 5 illustrates an exemplary synthetic airport background map.FIG. 6 illustrates an exemplary aerial orthophoto background map. FIG. 7illustrates an exemplary synthetic vision system (SVS) view backgroundmap. Other suitable background maps are also contemplated to suitdifferent applications.

Returning now to FIG. 2, an important aspect of the present AGDB is thatit is designed to generate smooth ground trajectories for the aircrafttaxiing operations. Specifically, the ground trajectories are continuous(without holes or gaps), and a derivative of each route has no cusppoints (i.e., tangents continuity). Also, the taxi routes computed withthe present AGDB can be compatible with all aircrafts allowed on a givenairport. A corresponding geometrical dual of a node is called a point.However, a geometrical point does not necessarily have to have acorresponding logical dual (i.e., a node). There may only be aconstruction point necessary to define an associated curve. Ageometrical dual of a link is also defined by a continuous set ofcurves. Further, each curve has a logical dual (i.e., a link). One ormore curves can have the same logical dual, and thus the geometricaldual of the link may be a set of curves.

The present AGDB provides a pre-computed connectivity list for each linksuch that each link realizes to which links and via which nodes the linkis connected. Further provided in the present AGDB is a pre-computeddual relationship between the geometrical and logical duals. Forexample, each point realizes its associated dual node (if the dual nodeexists), and each node realizes its associated dual point (as the dualpoint always exists). This configuration is similarly constructed andarranged for a curve-link pair and a link-element pair in the AGDB. Itis contemplated that the present AGDB is built manually, but using othersuitable dedicated software tools is also contemplated.

In a preferred embodiment, the present AGDB includes metadata having anInternational Civil Aviation Organization (ICAO) 4-letter AirportIdentifier, date, author, source origin of the AGDB, accuracy andintegrity of data, projection used (e.g., earth coordinates formapping), comments, and the like. The present AGDB further includes aset of lists of points, curves, nodes, links, and airport elements,which are described in greater detail below.

Referring now to FIG. 8, each control point is a geometrical punctualobject defined by at least one of a unique point identifier, a set ofcoordinates, a dual node identifier, a list of curves using this point,and the metadata as described above. In one embodiment, the coordinatesinclude latitude, longitude, and altitude locations in earth coordinates(e.g., World Geodetic System (WGS84) referential), or X/Y/Z axis valuesin projected coordinates.

Each curve is a geometrical linear object defined by at least one of aunique curve identifier, a set of control points identifiers, a duallink identifier, a curve length, and the metadata as described above. Alist of control points identifiers having a curve length of four (4) hasfour control points. Thus, in case of a segment having a 1^(st) orderBézier curve, inner control points can be set to −1. For example, thelist of control points identifiers [25 64 95 32] defines a 3^(rd) orderBézier curve (BC3), and [75 −1 −1 12] defines a 1st order Bézier curve(BC1).

FIG. 8 shows an exemplary geometric part of the flow graph with asatellite background map. Points are designated, for example, 1457,1477, 1474, 1473, etc. Curves are designated, for example, 1030, 1032,1028, 1034, etc. For example, the curve 1798 is defined by points 2704and 2705.

Referring now to FIG. 9, each node is a logical punctual object definedby at least one of a unique node identifier, a node type, a dual pointidentifier, a list of links using this node, and the metadata asdescribed above. In one embodiment, the node type includes at least oneof a switching point, a dead-end, a parking stand, a deicing point, astop, and a change of characteristics (e.g., PCN, a maximum wingspan).It is preferred that each node has a corresponding dual point.

Each link (or edge) is a logical linear object defined by at least oneof a unique link identifier, an initial node identifier, a final nodeidentifier, a list of dual curves identifiers, an element identifierdefined by the link, a link length, a link direction, a list ofconnectivity of the link, and the metadata as described above. It isalso contemplated that other suitable attributes are additionally usedfor defining the link, such as a max curvature of the link, a PCN of thelink, and a maximum wingspan allowed on the link. At least one list ofdual curves identifiers is included in the link for describing ageometrical path joining the initial and final nodes. The link directioncan be either one-way or two-ways, where the order of the one-waydirection (e.g., direct or inverse) is defined by the initial node andthe final node. A list of doublets [Id_Link, Id_Node], representing theconnectivity of the link, is interpreted as that the aircraft can travelfrom the current link to the Id_Link via Id_Node, which is common toboth links, with a smooth trajectory without holes and cusp points.

Each element is a logical linear object defined by at least one of aunique element identifier, an element type, an element name, a list ofnode identifiers, a list of link identifiers, and the metadata asdescribed above. The element type may include a taxiway, a runway, aparking line, and the like. The element name may be defined as <<14L>>for a runway, but other suitable symbols are also used to describedifferent airport elements to suit the application. The list of nodeidentifiers included in the element must have at least two nodeidentifiers, and the list of links identifiers included in the elementmust have at least one link identifier for describing a logical path tojoin successive nodes.

FIG. 9 shows an exemplary logical part of the flow graph is shown. Nodesare designated, for example, 183, 271, 268, 269, 213, etc. Links aredesignated, for example, 303, 299, 296, etc. Elements are designated,for example, 22 [S8], 25 [M8], etc. For example, the element 25 (namedM8) is defined by the set of links 298, 651, and 652. Link 295 isdefined by nodes 270 and 269. As shown in FIGS. 8 and 9, a correspondingdual point of node 466 is point 2704 (FIG. 8), and a geometrical supportof link 298 is the curve 1028 (FIG. 8).

FIG. 10 shows exemplary exhaustive potential trajectories indicated byarrows on the on-board display even if the trajectories are notphysically painted on the airport ground. As discussed above, the AGDBbuilt by the present taxiing path optimization system 10 represents adescription of all potential taxi ground trajectories or routes thatcould take the aircraft, using a geo-referenced geometrical descriptionand a logical flow graph description, including taxiways, runways,parking areas, deicing points, and the like.

Referring now to FIG. 11, connectivity examples are shown using theBézier curves. For example, the 1st order Bézier curve 1 (i.e., astraight line or a segment) is defined by two points 1 and 2, and the 3′order Bézier curve 2 is defined by four control points 3, 4, 5, and 6.The first and last control points are always on the curve.

Referring now to FIG. 12, an exemplary connectivity link is shown. Forexample, link 2 is connected to link 1 via node 1, also to link 3 vianode 1, also to link 4 via node 1, also to link 6 via node 7, and alsoto link 7 via node 7. Notably, link 2 is not connected to link 5 vianode 1 because Node 1 is a cusp point for a trajectory traveling fromlink 2 to link 5. Thus, link 5 is excluded from the pre-computedconnectivity list.

Referring now to FIG. 13, in a preferred embodiment, the present AGDB isbuilt with a set of predetermined rules. Exemplary rules includeenforcing continuity of tangents at each point, and curvatureconstraints for limiting a minimal local radius of a curve such that theresult curve is smooth and representative of a potential trajectory ofthe aircraft on the ground. For example, the curve 2 is built so thatits tangent at point 3 (represented by segment [3, 4]) is aligned withcurve 8. As a result, point 3 is not a cusp point or a break point for atrajectory traveling from curve 8 to curve 2, thereby leading to asmooth trajectory. Identical building rules are applied at points 6 and11.

Returning now to FIG. 2, in step 200, the present taxiing pathoptimization system 10 determines a final or modified taxi clearancebased on an initial taxi clearance inputted by the crew or received fromother related systems. Initially, the pilot (or the flight crew) mustenter the clearance into the present system 10 using the keyboard orother suitable tactile interactive devices for computing thecorresponding taxi route on the digital map for display. If the taxiclearance contains two elements, then these clearance elements arenecessarily the departure and the destination. In this case, there is noambiguity, and the taxi clearance is computed as inputted.

However, if the taxi clearance contains at least three elements, thepresent system 10 computes two taxi routes, considering both taxiclearance types (i.e., the destination is the last element, or thesecond element in the taxi clearance). An exemplary method isillustrated in step 500 below for computing a taxi route based on theinputted taxi clearance. The present system 10 determines or finalizesthe taxi clearance based on the inputted taxi clearance. For example,when the present system 10 does not find any acceptable solution for theinputted taxi clearance due to a database or system error, a taxiclearance data input error, or an impossible taxi clearance error, thepresent system generates a warning signal or message to the flight crewfor a corrective action.

When there is only one taxi route solution available for the taxiclearance, the present system 10 selects the solution as the final taxiclearance, but when there are multiple taxi route solutions available,the present system selects one of the solutions based on a set ofpredetermined criteria. In one embodiment, the predetermined criteriainclude at least one of a shortest length, and a smallest number ofairport elements, which are not explicitly entered by the crew in itsinitial clearance. When the present system 10 determines the final taxiclearance, the present system proposes a consolidated taxi clearance tothe crew for validating the proposal. In one embodiment, the proposedtaxi clearance may be reordered, and be used as an input to otherrelated systems, such as a system for computing the taxi route, or otherguidance applications.

In step 300, the flight crew enters a taxi clearance by inputtingclearance elements into the present taxiing path optimization system 10using the keyboard or other suitable tactile interactive devices, suchas the Smart Finger and the voice recognition system, and the like. Itis preferred that at least four types of operations are performed by thepresent system 10, namely Add, Insert, Modify, and Remove.

The Add operation refers to adding a new clearance element at the end ofthe taxi clearance, where the addition of the new element is performedat the end of the pre-existing clearance element sequence. The Insertoperation refers to inserting the new clearance element into the taxiclearance. For example, the insertion of the new element in the middleof the clearance is achieved by pinching two fingers between twoelements already entered, and then selecting the new element to beinserted directly on the map or by typing the identifier on a virtualkeyboard.

The Modify operation refers to revising the element of the taxiclearance. For example, the crew selects the clearance element on thedisplayed clearance sequence text, and then enters the new element toreplace the selected element. The Remove operation refers to deletingthe selected element from the taxi clearance. When one of the fouroperations is performed, the present system 10 or a subsystem of thepresent system, such as a taxi clearance manager 18, updates the taxiclearance, and sends the updated sequence to another subsystem of thepresent system, such as a taxi route generator 20. For example, the taxiroute generator 20 computes or creates a taxi route, which is displayedfor the flight crew, and a consolidated taxi clearance, which is alsodisplayed for the flight crew to fill any gaps or holes in the clearancesequence as desired.

In a preferred embodiment, the present system 10 provides a guidinginterface system 22. An important feature of the guiding interfacesystem 22 is that it provides an unelectable look and feel fornonexistent labels on the keyboard. For example, if the airport haselements with alphanumeric labels beginning with a character from “A” to“S” only (plus numeric values concatenated at the end), then the guidinginterface system 22 causes the keys from “T” to “Z” unselectable fromthe keyboard because these keys are not being used in the present system10.

It is preferred that the present AGDB collects a list of all possibleelements of the airport, and saves the list in memory for later use.Thus, as the flight crew enters letters and numbers into the presentsystem 10 as part of the taxi clearance sequence, the guiding interfacesystem 22 selectively invalidates the keys from the keyboard based onthe saved element list. For example, if the saved element list includeselements beginning with a letter “P,” such as P20, P30, P40, P60, P70,and the pilot has already entered “P”, then the guiding interface system22 causes the keys having numbers “0,” “1,” “5,” “8,” and “9”unselectable or invalid because such numbers do not follow the letter“P” as evidenced in the element list. This invalidation methoditeratively applies to the rest of characters in each element.

Another important feature of the guiding interface system 22 is that,after each clearance element is entered into the present system 10, theguiding interface system 22 automatically detects airport elements(whether adjacent or not) and creates a pre-filter by highlightingcorresponding labels on the digital map for considering precision of theaircraft position. These highlighted elements attract and guide the crewduring taxi clearance operations. It is noted, however, that the guidinginterface system 22 does not prevent a selection of other elements nothighlighted or not directly connected to the current element. In anotherembodiment, the keyboard highlights all elements from an airport whetherthey are adjacent are not. This creates a pre-filter that limits thenumber of possible inputs without being too restrictive. In some cases,adjacent elements are rarely given in a taxi clearance.

In a preferred embodiment, to accelerate a manual entry of the clearanceelement name on the keyboard, the guiding interface system 22 highlightsall possible combinations of letters and numbers following a precedingcharacter. For example, if the possible next elements are W40, W50, andY50, the guiding interface system 22 highlights the letters “W” and “Y.”Subsequently, if the crew enters the letter “W,” the guiding interfacesystem 22 highlights the numbers “4” and “5.” Next, if the crew entersthe number “5,” the guiding interface system 22 highlights the number“0” only since “W50” is the last possible next element.

As such, the guiding interface system 22 computes the list of nextpossible elements at each character entry. More specifically, theguiding interface system 22 determines the last link of the current taxiroute. The taxi route generation process is described in greater detailbelow in relation to step 500. Also, the guiding interface system 22follows each link connected to the last link of the taxi route until alink associated with an element is found. The guiding interface system22 saves the name of each element found in the element list, and theelement list is used to highlight the element labels or keys asdescribed above.

Referring now to FIGS. 14-21, an exemplary Smart Finger system is shown.An important feature of the Smart Finger system is that a user may drawa path on a digital display with a fingertip, but other suitabledevices, such as a mouse, a digital pen, and the like, are contemplatedto suit the application. FIG. 14 illustrates that the user (e.g., apilot or a flight crew) selects an initial taxiway S50 by clickingdirectly on a taxiway element shown on the digital display. FIG. 15illustrates that the Smart Finger system provides a feedback to the userby highlighting or coloring the selected taxiway S50, for example, ingreen. Also, the element name S50 is displayed on a command linedisposed at the bottom of the display for convenience. Otherorientations of the command line are also contemplated.

FIGS. 16 and 17 illustrates that the user can also enter a next taxiwayM4 using a virtual keyboard instead of clicking directly on the taxiwayelement. The virtual keyboard may be used when the next taxiwayidentifier is out of range or not shown on the display. FIG. 18illustrates that the user confirms the inputted element name by clickingon the Enter button on the virtual keyboard. The Smart Finger systemconfirms the validity of the element name M4 against the present AGDB,and displays the element name M4 as a solid entry in the command line ofthe display.

FIG. 19 illustrates that the present system 10 proposes an optimal taxirouting between the inputted element names (e.g., as the departure anddestination points) by displaying element names that are different fromthe inputted element names. For example, the elements W40, S4, and 32Lare inserted between the inputted elements S50 and M4, and the taxiroute having the elements S50, W40, S4, 32L, M4 is highlighted on thedisplay for confirmation. The taxi route selected by the present system10 is then validated by clicking on the Check button on the virtualkeyboard.

FIGS. 20 and 21 illustrate an exemplary raw drawing method for inputtingthe taxi clearance on the display using the Smart Finger system. In oneembodiment, the Smart Finger system includes a tactile fingerinteraction device with a touch-sensitive screen using the present AGDBfor recognizing the inputted taxi clearance. As shown in FIG. 20, theuser draws a line directly on the digital map using a dedicated inputdevice, such as the finger tactile interaction device, thetouch-sensitive screen, a digital pen and pad, a mouse, a trackball, andthe like. Optionally, the user enters a desired taxi clearance in anedition mode. This raw drawing does not have to be accurate because theSmart Finger system recognizes general positions and directions of theline on the digital map in terms of taxi clearance sequence. The line ishighlighted in a first color, e.g., yellow.

FIG. 21 illustrates that the Smart Finger system may recognize theclearance portion drawn by the user, or may propose a different computedtaxi clearance based on the raw drawing. More specifically, the rawdrawing is converted into a vector of map coordinates. For example, theSmart Finger system records all successive finger positions in screencoordinates during the raw drawing process, and then computes, for eachposition on the display, a position on the digital map inlatitude-longitude coordinates, or in metric coordinates. Alternatively,the X/Y coordinate vector in map coordinates can be used. An exemplaryfinger position vector may include the X/Y coordinates of [103.5 56.3][103.7 56.1] [104.3 55.4] . . . [152.3 26.1]. As an example, thesecoordinate numbers represent X/Y coordinates inputted by the user, andFIG. 21 illustrates a succession of two-dimensional points. These X/Ycoordinates may be expressed in a reference system of the underlying map(e.g., in meters with respect to a given reference point), or may beexpressed in pixels with respect to the screen coordinates.

In a preferred embodiment, the Smart Finger system executes a predefinedalgorithm to generate a set of successive element identifiers forrepresenting the recognized taxi clearance sequence. As an example, foreach finger position indexed i in the coordinate vector, the SmartFinger system computes a path tangent vector PTV at the correspondingindex. The path tangent vector PTV may be defined as provided byexpression (5):

$\begin{matrix}{{PTV} = \frac{\left\lbrack {{x\left( {i + 1} \right)} - {{x\left( {i - 1} \right)}{y\left( {i + 1} \right)}} - {y\left( {i - 1} \right)}} \right\rbrack}{{norm}\left( {{{x\left( {i + 1} \right)} - {x\left( {i - 1} \right)}},{{y\left( {i + 1} \right)} - {y\left( {i - 1} \right)}}} \right)}} & (5)\end{matrix}$

where x and y denotes the X/Y coordinates, and norm denotes anormalization function. In one embodiment, the normalization function ofexpression (5), namely norm(x(i+1)−x(i−1), y(i+1)−y(i−1)), may bereplaced with another exemplary denominator fraction as a divisor, suchas √{square root over ((x(i+1)−x(i−1))²+(y(i+1)−y(i−1))²)}.

Also, for each finger position, the Smart Finger system finds all curveslocated in a predetermined range or threshold around the position atindex i. This operation can be performed by computing a distance betweenthe point at index i and each curve in the AGDB. If this distance isless than the predetermined threshold or within the predetermined range,the curve is within an acceptable range of the finger point. Optionally,this operation can be performed using a quad tree algorithm to improvecurve search performances.

For each curve found, the Smart Finger system computes the tangentvector at a middle point of the curve. Optionally, other suitablelocations on the curve can be used in computing the tangent vector tosuit different applications. If an absolute value of dot product of thistangent vector and a previously computed path tangent vector at index iis greater than a predetermined threshold, and if the curve isassociated to a link that is associated to an element, then the SmartFinger system saves the element identifier in memory for later use.However, the Smart Finger system removes duplicate element identifiers.A tuning or calibration of the predetermined threshold can be performedmanually or automatically to achieve desired results.

During this operation, if only one element identifier is found, and ifthis identifier has not yet been found for another index k, then theSmart Finger system adds or consolidates this element identifier to therecognized clearance sequence. At the end of the algorithm for eachfinger position, the Smart Finger system has computed the set ofsuccessive element identifiers that represents the recognized taxiclearance sequence. In certain embodiments, this consolidated taxiclearance sequence may be used in conjunction with other user inputdevices, such as a keyboard, or an individual element selection methodas described above in relation to FIGS. 14-21, for computing anddisplaying the taxi route.

Then, in this example, the Smart Finger system highlights finalizedelements W50, W40, W30, W20, S2, M2, and N2 on the digital map in asecond color, e.g., green, for confirmation. For example, the colorchange into green occurs only once after the confirmation of the entiretaxi clearance by the user. As a result, this raw drawing method reducestaxi operation time and costs due to its speedy input method andinteraction with the airport database, such as the AGDB and the ARINC816 databases.

Returning now to FIG. 2, in step 400, the present taxiing pathoptimization system 10 defines or determines a current aircraftposition. Optionally, step 400 can be performed before or in parallelwith step 200. Further, step 400 can be performed at an on-groundsystem, such as the ATC Ground Control system. The present taxiing pathoptimization system 10 determines an ownship position by consolidatingadditional data from other sources for preventing an inaccurate displayof the aircraft and airport elements on the digital map. In oneembodiment, the additional data include airport databases, such as theARINC 816 databases and AGDB.

An ownship symbol is displayed on a presumed centerline of the runway ortaxiway on which the aircraft is currently traveling. In one embodiment,the ownship symbol is displayed with a fixed uncertainty ring inaccordance with a precision of the GNSS receiver. Similarly, othersurrounding aircraft and airport element symbols are presumablydisplayed on the centerlines of the corresponding runways or taxiways. Aconsolidated position of the aircraft is determined based on positionalinformation received from the airport databases. The consolidatedposition of the aircraft is displayed on the on-board display, such asan electronic map showing the ownship symbol and other aircraft symbols.

In one embodiment, the present system 10 identifies an existing taxiroute (e.g., a computed taxi route) to improve the consolidation ofaircraft position and aircraft heading parameter for providing aircraftheading information. Preferably, the present system 10 uses the AGDB asthe flow graph database of the airport, having access to raw aircraftpositions, for computing a consolidated aircraft position. In oneembodiment, the present system 10 performs five steps to compute theconsolidated aircraft position. For example, in the first step, thepresent system 10 finds all curves located within a predetermined rangearound the aircraft position. This can be achieved by computing adistance between the aircraft position and each curve in the AGDB. Ifthe distance is less than a predetermined threshold, the curve isdetermined to be within the range of the aircraft. Other suitablealgorithms, such as a quad tree algorithm, are used to improve the curvesearch performances.

In the second step, if no such curve is found, the present system 10stops the consolidation computation, and outputs the raw aircraftposition or heading parameter, or provides no output data. In the thirdstep, if at least one such curve is found, the present system 10computes a penalty value for each curve found. In the fourth step, thepresent system 10 selects a curve having the lowest penalty value. Inthe fifth step, the present system 10 computes the consolidated aircraftposition and heading parameter based on the selected curve.

The penalty value is determined based on a combination of severalpredetermined criteria. For example, the penalty value is computed basedon a distance d between the aircraft position and an orthogonalprojection of the aircraft position on the corresponding curve, and anangular deviation W between the aircraft heading and the tangent vectorof the corresponding curve at the projection of the aircraft position onthe corresponding curve. For example only, an exemplary penalty value Pmay be defined as provided by expression (6):

P=k _(d) d+k _(ψ) ψ+δk _(route)  (6)

where ∂=0 if the curve is part of the current taxi route, and 1otherwise. k_(d), k_(ψ), k_(route) denote coefficients having weightingfactors used to give predetermined weights (e.g., for different effects)of each term of the penalty computation.

Referring now to FIG. 22, an exemplary method of determining aconsolidated aircraft position is illustrated using the five stepsdescribed above. For example, the present system 10 finds three curvesCurve i, Curve j, and Curve k within the predetermined range Rangearound the aircraft indicated by a triangle Δ. The present system 10computes three distances, d_(i), d_(j), and d_(k) between the aircraftposition and the orthogonal projection of the aircraft position on eachfound curve. A computational method of the projection of a point on acurve depends on a type of the curve, and can be performed as known inthe mathematics art. The present system 10 computes three angulardeviations Ψ_(i), Ψ_(j), and Ψ_(k) using any computational method knownin the art.

Next, the present system 10 selects one of three curves Curve i, Curvej, and Curve k, based on the k_(d), k_(ψ), and k_(route) values. Thek_(d), k_(ψ), and k_(route) values may be empirically tuned (e.g., bygiving similar weights of d, psi, and delta) for achieving a desiredconsolidation aircraft position. In this example, the Curve j may havethe lowest penalty value than the Curve i and Curve k because the Curvej is part of the current taxi route. The present system 10 selects theCurve j as the consolidated aircraft position and heading parameter,which is indicated by an arrow in red.

Referring now to FIG. 23, if the present system 10 does not find anytaxi route near the aircraft, the most likely consolidated aircraftposition is computed based on a network of curves from the AGDB.Similarly, the aircraft heading is also consolidated based on thenetwork of curves from the AGDB.

Referring now to FIG. 24, if the present system 10 finds a taxi routenear the aircraft, the present system improves the consolidation of theaircraft position and heading based on the network of curves. Thus, aresult of the consolidation can be different according to whether anearby trajectory is absent (FIG. 23) or present (FIG. 24). Although areal position of the aircraft is unknown to the present system, ameasured position is available based on the signals received from thededicated sensors and navigation systems. A consolidated position of theaircraft represents an improved measured position of the aircraft basedon the AGDB data.

In another embodiment, the present system 10 identifies an aircraftground speed parameter (if available) to temporarily compute theconsolidated aircraft position or aircraft heading parameter even ifmeasured aircraft position or aircraft heading parameter areunavailable. As an example, the aircraft position is determined based onthe latitude/longitude values in the WGS84 reference system. Also, theheading parameter denotes the heading of the aircraft. Theses parametersare measured, for instance, by the IRS and GNSS sensors.

When the aircraft ground speed is known, the present system 10 uses theground speed of the aircraft to estimate the aircraft position andheading parameters in case of temporary unavailability of the headingparameters. In some cases, these parameters may become unavailable dueto unavailable GNSS signals or excessive drift of the IRS position.

For example, if the X/Y coordinate vector in map coordinates is used,and X_(a), Y_(a), and Ψ_(a) denote the last available measurements ofthe aircraft position and heading, the present system 10 computes anestimation of the aircraft position and heading using the followingequation (7):

$\begin{matrix}\left\{ \begin{matrix}{X = {X_{a} + {{V \cdot t \cdot \cos}\; \psi_{a}}}} \\{Y = {Y_{a} + {{V \cdot t \cdot \sin}\; \psi_{a}}}}\end{matrix} \right. & (7)\end{matrix}$

where V is the aircraft current ground speed, and t is the time elapsedsince the measurements were unavailable.

Thus, if a taxi route is available as shown in FIG. 24, the presentsystem 10 may use the taxi route to improve the quality of theestimation. For example, the present system 10 estimates the aircraftposition and heading based on assumption that the aircraft has travelleda distance equal to V·t along the taxi route from a last known aircraftposition.

This method enables the present system 10 to temporarily (e.g., severalseconds) compute the consolidated position and heading parameter even ifthe measured position and heading parameter are unavailable. If theaircraft position and heading measurements are still unavailable after apredetermined period, the present system 10 stops the estimation processas the estimation results may diverge from true aircraft position andheading parameter. As such, this method provides an enhanced continuityof service to the flight crew in case of temporary loss of the GNSSsignal. In one embodiment, parameters giving the quality of the receivedsignal inside the GNSS receiver can also be used to remove the ownshipsymbol in case of a significant deviation. Exemplary parameters includeHDOP (Horizontal Dilution of Precision) and HIL (Horizontal IntegrityLimit) parameters. Returning now to FIG. 2, in step 500, the presenttaxiing path optimization system 10 generates or computes a taxi routebased on an inputted taxi clearance. The inputted taxi clearance doesnot have to be complete or continuous because the present system 10completes automatically the missing clearance elements as needed. Forexample, the present system 10 indicates to the flight crew that thepresent system has automatically inserted missing clearance elementsduring a taxi route computation or generation phase such that the crewcan take an appropriate action, such as to accept, confirm, or validatethe inserted elements, reject the inserted elements, or modify the taxiclearance.

The present system 10 identifies aircraft capabilities, such as the ACN,PCN, maximum turning radius and maximum wingspan, for preventing fromgenerating or selecting taxi routes that are incompatible with aircraftcharacteristics, and generates a warning signal (such as a coding color)or message for the flight crew when such incompatibilities are found inany taxi routes, such as an initial inputted taxi clearance, or afinalized or computed taxi clearance. Further, the present system 10suggests the flight crew different taxi route alternatives when the taxiclearance is ambiguous, such that the crew can selectively choose one ofthe alternatives.

These computed taxi routes are designed to support other relatedsystems, such as the on-ground guidance system for the aircraft, andensure data accuracy and integrity using airport flow graph databases,such as the AGDB and ARINC 816 databases. The present system 10 maysimply display the taxi route on the digital map using suitablegeo-referenced background charts, synthetic view, or satellite images.As discussed above, the taxi clearance may be entered into the presentsystem 10 using a keyboard, a datalink, or other suitable electronicdevices known in the art.

Referring now to FIG. 25, an exemplary method of computing or generatinga final taxi clearance and corresponding taxi routes is illustratedusing the present AGDB and the present system 10. Although the followingsteps are primarily described with respect to the embodiments of FIG. 2and other related methods, it should be understood that the steps withinthe method may be modified and executed in a different order or sequencewithout altering the principles of the present disclosure.

The method begins at step 2500. In step 2500, an initial taxi clearancehaving a list of taxi clearance elements is inputted by a user orreceived by the present system 10, which contains element names (e.g.,<<P60 P50 T50 E E21>>) or identifiers (e.g., <<105 925 32 412 223>>). Instep 2510, the present system 10 searches for a path or link betweensuccessive pairs of nodes using an algorithm known in the art, such asDijkstra or A* algorithms. A continuous set of links is generatedconnecting from one node to the next node. The path or link found iscomputed for minimizing a predetermined set of criteria, e.g., forminimizing the length of the path.

Other criteria include minimizing the risks associated with the aircraftcharacteristics and the airport capabilities, such as the ACN, PCN, andmaximum wingspan. It is contemplated that the present system 10 searchesfor a path with the smallest taxi route length or the smallest time totravel through the taxi route, or the smallest number of airportelements. As a result, a set of lists of links is generated (i.e., onelist of links for each pair of nodes). Preferably, the taxi clearanceinput does not need to be continuous. Thus, when there are gaps betweentwo successive elements in the clearance, the gaps are automaticallyfilled by the present system 10 while finding the path between theelements.

Referring now to FIGS. 26 and 27, an exemplary method of searching for apath between successive pairs of nodes is illustrated. In this example,the present system 10 identifies a first or current node in the list oflinks, which may be a departure gate node (e.g., taxi-out), or athreshold of a current runway (e.g., taxi-in). Generally, if theaircraft is traveling on a taxiway in the airport, the present system 10chooses an extreme node (e.g., a beginning or ending node) of theairport element behind the aircraft. If the aircraft position andheading are unknown, the present system 10 chooses an arbitrary extremenode.

From this first or current node, for each element of the taxi clearance,the present system 10 computes a first route from the current node to afirst node of the next element. If the first route has a last node ofthe next element, the last node is selected as the current node at anext iteration. Otherwise, the present system 10 computes a second routefrom the current node to the last node of the next element. If thesecond route has the first node of the next element, the first node isselected as the current node at the next iteration. Otherwise, there isan ambiguity. As discussed above, the first and last nodes are definedby the nodes list of the corresponding element.

As an example, in FIG. 27, each of two elements designated 62 and 12 hasone or more links. Specifically, the element 62 is composed of the link23, but the element 12 is composed of links 32, 73, and 68. As theaircraft heading and position are known in this example, the presentsystem 10 selects node 1 as the first node. Then, the present system 10computes a first route from node 1 to node 3 (i.e., the first node ofelement 12). The resulting first route includes links 23-45-68 havingnode 3 as the last node of element 12. Thus, node 4 becomes the currentnode as a new starting node for the next iteration.

Next, the present system 10 computes a second route from node 1 to node5, because the node 5 is not included in the first computed route,causing the ambiguity of the clearance. Thus, both first and secondroutes are computed and displayed, but there exists a bifurcation point(node 2). The present system 10 selects a last common node of both taxiroutes as the current node at the next iteration, which is the node atwhich both compute taxi routes bifurcate.

As an example, in FIG. 27, the present system 10 searches for a pathfrom node 1 to node 5, then to node 3. The present system 10 selectsnode 2 as the current node for the next iteration, which is the lastcommon node for both routes having links 12, 45. For the last element ofthe taxi clearance, if two taxi routes are available, the present system10 displays both routes to indicate the ambiguity to the flight crew.

Returning now to FIG. 25, in step 2520, the present system 10 examineswhether each link is compatible with the aircraft characteristics. Forexample, the present system 10 checks if the ACN is smaller than thelink PCN, or checks if the aircraft wingspan is smaller than the linkmaximum wingspan. When incompatibilities are found, the present system10 generates a warning signal or message for the flight crew, or avoidsthe link during the search so that the final path does not include thislink.

In step 2530, the present system 10 concatenates the successive set ofcontinuous links into a single list of successive links, from thedeparture point to the destination point through possible or eligiblewaypoints. Specifically, the present system 10 computes a list ofsuccessive elements associated with the single list of successive linksbased on the initial taxi clearance. The present system 10differentiates the elements inputted by the flight crew from theelements automatically generated by the present system for filling inthe gaps between unconnected airport elements (e.g., color-codeddifferently).

In step 2540, the present system 10 consolidates the inputted elementswith the generated elements, and displays the consolidated taxiclearance without the gaps. An exemplary display of the consolidatedtaxi clearance is illustrated in FIGS. 28 and 32.

Referring now to FIG. 28, a first row represents the initial clearanceelements W90, P70 inputted by the flight crew. A second row representsthe computed clearance sequence having the automatically generatedelements W80, S8, M8, N8 for filling in the gaps between the initialclearance elements W90, P70. A third row represents the displayedclearance sequence having the initial clearance elements color-coded ina first color (e.g., magenta), and the automatically generated elementsin a second color (e.g., blue).

Returning now to FIG. 25, in step 2550, the present system 10discretizes the list of links into X/Y points. A list of X/Y pointsconstitutes a final taxi route representation, and may be displayed onthe digital map. It is also contemplated that the list of points areused for other applications, such as the aircraft guidance applications.The present system 10 converts each link into a set of curves, which arethe geometrical duals of the links.

Referring now to FIG. 29, as an example, link 18 has curves 1475, 1477,1476, 1474, 1473, and 1468. Each 3rd order Bézier curve is approximatedto be a succession of segments using any approximation technique knownin the art. Further, an empirical tuning can be performed for selectingan acceptable value. As an example of the empirical tuning, a firsttuning is performed to have a smooth display of turns. An exemplaryacceptable value for the first tuning is 30. A second tuning isperformed to display performances (but poor smoothness). An exemplaryacceptable value for the second tuning is 10.

Referring now to FIGS. 30-35, an exemplary taxi clearance input methodis illustrated using the Smart Finger system. More specifically, FIGS.30-32 show an exemplary method of displaying the consolidated taxiclearance. FIG. 30 shows an empty clearance sequence on the command linedisposed at a bottom of the display. FIG. 31 shows that a clearanceelement W50 is entered by directly clicking on the element W50 using afingertip of the flight crew. The first element of taxi clearance isdisplayed on the command line. FIG. 32 shows that the next element S2 isselected and entered by the flight crew as a second clearance element.As discussed above, the present system 10 consolidates the inputtedelements W50 and S2 with the generated elements W40, W30, W20, anddisplays the consolidated taxi clearance without the gaps. All missingclearance elements are automatically inserted by the present system 10.

FIGS. 33-35 illustrate an exemplary method of resolving an ambiguoustaxi clearance in the present system 10 using the Smart Finger system.FIG. 33 shows that an element T50 is entered or selected by the flightcrew in addition to a previously selected element P50, both of which arehighlighted for identification. In this example, the clearance elementsinclude P70, P60, P50, and T50 as displayed in the command line at thebottom of the display. The clearance element T50 appears at an end ofthe consolidated clearance sequence P70, P60, P50, T50. FIG. 34 showsthat a next element E is selected or entered by the flight crew.However, from the element T50, the taxi route is bifurcated to the leftside and the right side relative to the element T50, thereby creatingthe ambiguity. The present system 10 proposes these two possible taxiroutes to the flight crew, and the ambiguity is resolved by the nextelement chosen by the flight crew. For example, as shown in FIG. 35, thecrew selects or enters the next element E21 (e.g., a parking stand) toresolve the ambiguity. As a result, the final taxi clearance isestablished as a set of elements P70, P60, P50, T50, E, and E21.

While preferred embodiments of the disclosure have been hereinillustrated and described, it is to be appreciated that certain changes,rearrangements and modifications may be made therein without departingfrom the scope of the disclosure.

What is claimed is:
 1. A method of computing a taxi route for anaircraft, the taxi route representing an on-ground trajectory of anairport during taxiing operations utilizing a taxiing path optimizationsystem, the method comprising: receiving an initial taxi clearancehaving a list of taxi clearance elements including at least two airportelements; searching for links between successive pairs of nodes definedby the list of taxi clearance elements using a predetermined algorithm;generating a set of links connecting the nodes based on the searchedlinks; automatically generating at least one airport element for fillingin gaps between unconnected airport elements; consolidating the initialtaxi clearance with the generated airport elements; and discretizing theset of links into X/Y points as a final taxi route representation forthe aircraft.
 2. The method of claim 1, wherein the set of links isgenerated based on aircraft characteristics and airport capabilities. 3.The method of claim 1, wherein the link between the successive pairs ofnodes is searched based on at least one of a taxi route length, a traveltime in the taxi route, and a number of airport elements in the taxiroute.
 4. The method of claim 1, further comprising computing a list ofsuccessive elements associated with the single list of successive linksbased on the initial taxi clearance.
 5. The method of claim 1, furthercomprising computing a taxi path based on the set of links byconcatenating continuous links into a single list of successive links,the taxi path having a departure point and a destination point throughpossible waypoints.
 6. The method of claim 1, further comprisinggenerating a warning signal or message when incompatibility is detectedin the taxi route, and preventing the generation of a finalized taxiroute that is incompatible with airport elements based on at least oneof: an Aircraft Classification Number, a Pavement Classification Number,a turning radius and a maximum wingspan of the aircraft.